Tumor cells have been characterized by the phenotypes expressed on cell surface membranes. Previously, defective synthesis of glycolipids, lack of contact-dependent enhancement of glycolipid synthesis, and the change of surface glycosyl label, particularly the loss of "galactoprotein a" and the appearance of "ceramide X", were shown to be the characteristic phenotypes of transformed cells. This proposal is for further studies on: (1) details of structural change and the mechanism of glycolipid synthesis and degradation in relation to control of cellular interaction, cell cycle, and cell proliferation; and the deficiency of such control mechanism on transformed cell membranes; (2) chemical and immunological characterization of surface-exposed glycolipids and glycoproteins (e.g., "ceramide X" of NILpy cells and "galactoprotein a" of NIL and BHK cells) in relation to immunogenicity of these surface components, and the use of surface specific components in studying immuno-suppression of tumor development and of blocking cell-mediated immunity; (3) surface modification of cells and concurrent changes of cell physiology by applying purified anti-glycolipid antibodies and by an artificial enrichment of a special glycolipid in membranes; a possible control of tumor cell growth through such surface modification will also be studied; (4) comparative surface profile as to glycolipids of genetically related cells showing high and low tumorigenicities and/or high and low metastatic properties. The long-term goal of these studies is to determine the role of cell surface heteroglycans which ultimately may provide clues for the control of cancer.